Much talk of carbon monoxide, say (3)
I believe the answer is:
gas
'much talk' is the definition.
'gas' can be an answer for 'talk' (gas can mean to chat). I'm not certain of the 'much' bit.
'carbon monoxide say' is the wordplay.
'carbon monoxide' becomes 'g' (I can't justify this - if you can you should give a lot more credence to this answer).
'say' becomes 'as' (I've seen this in other clues).
'g'+'as'='GAS'
'of' is the link.
Can you help me to learn more?
(Other definitions for gas that I've seen before include "It's not liquid or solid, like American petrol" , "Chatter (colloq.)" , "Fuel; idle talk" , "What's needed to drive" , "Hydrogen or methane, say" .)